Liquid Lens Patent by Canon (and video)

Ever heard about liquid lenses? It may be the next big thing in optical engineering. Basically, liquid lenses work by applying an electric voltage to an electrolytic solution (that’s the liquid) in order to curve its surface (called meniscus). You probably are already thinking: Hey, that means no moving parts! And you are right. Liquid lenses have a series of advantages over traditional lenses. Beside not having moving parts (and thus less mechanical parts), they respond quicker to electrical signals, they do not have a motor (you thought that USM was the big thing? Think again) and they are naturally much more silent. Just one quick note: Not having a motor means they need less electrical power, and that means the battery charge will last longer. There is a 10 minutes video at the end of the post that explains the technology. Fun to watch and good examples. Ok, let’s see the patent (it was very tiring to read :-)).

Canon filed a patent for a liquid lens that was published yesterday: The present invention relates to liquid lenses including an electrolytic solution containing iodide ions and apparatuses including such liquid lenses.

The abstract of the patent: A decrease in the spectral transmittance of a liquid lens due to yellowing of an iodide aqueous solution used as an electrolytic solution is inhibited. A liquid lens includes a liquid container, an electrolytic solution contained in the container and containing iodide ions and a water-soluble antioxidant that inhibits oxidation of the iodide ions, a nonelectrolytic solution contained in the container and forming an interface with the electrolytic solution, and an electrode configured to apply a voltage to the electrolytic solution. A voltage is applied across the electrolytic solution and the electrode to change the curvature of the interface.

The described lens is based on electrowetting, a procedure where electricity is applied to an electrolytic solution. I report some excerpts from the patent: Among several types of liquid lenses is one based on electrowetting (EW), which changes the angle between an interface between two liquids, namely, an electrolytic solution and a nonelectrolytic solution, and a solid paet in contact with the two liquids […] as a voltage is applied across the electrolytic solution and an electrode. […] An EW liquid lens includes an electrolytic (conductive) solution and a nonelectrolytic (nonconductive ) solution having different refractive indices and adjusted to similar specific gravities. These two solutions are sealed in a container to form an interface without mixing with each other. […] In the sealed state, a voltage applied across the electrolytic solution and an electrode layer disposed with an insulating layer therebetween changes the contact angle at the end of the interface between the two liquids without changing the volumes thereof. As the contact angle changes, the radius of curvature of the spherical interface changes correspondingly. This changes optical refractive power because of the difference in refractive index between the two liquids. […]

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